Light olefins such as ethylene, propylene and butylene serve as feeds for the production of numerous important chemicals and polymers. Typically, light olefins are produced by cracking petroleum feeds.
An alternative route for manufacturing light olefins is to catalytically convert oxygenates such as methanol to an olefin product. This conversion can be accomplished using a variety of molecular sieve catalysts. Several of these catalysts are highly selective in forming ethylene and propylene. However, a significant amount of water is formed as a natural by-product, and this water must be removed from the desired light olefin product.
U.S. Pat. No. 6,740,791 B2 discloses a process for converting an oxygenate to an olefin product. Water is removed from the olefin product using a quench tower to cool the product and condense the water. The olefin portion of the olefin product is recovered in an overhead stream from the quench tower, and the condensed water fraction is recovered as a bottoms stream. The condensed water fraction is recovered from the quench tower, and sent to a fractionator for separation into further streams.
U.S. Pat. No. 6,459,009 B1 discloses an alternative process for converting an oxygenate to an olefin product. Water is removed from the olefin product using a two-stage quench tower to cool the product and condense the water. The olefin product is passed to a first stage quench tower and contacted with an aqueous stream and a neutralizing agent introduced at the top of the quench tower to provide a hydrocarbon vapor stream and a first stage bottoms stream containing water. The vapor stream is cooled and sent to a second stage tower to further separate light olefins and additional water. A portion of the first stage bottoms stream is withdrawn as a drag stream, and another portion of the first stage bottoms stream is recycled to the first stage tower.
Removing water and other condensable materials from an olefin stream can be problematic. For example, water that is recovered should be relatively low in hydrocarbon components, and the recovered olefin compounds should be relatively free of water. In addition, systems for separating the condensable materials from the light olefin compounds should be low in maintenance and should be easy to operate. There is, therefore, a need to pursue more efficient ways of removing water and other condensable materials from olefin streams, particularly olefin streams high in light olefin content.